package projects.android.sms.util;

/**
 * Converts hexadecimal Strings.
 * 
 * @since 1.1
 * @author Apache Software Foundation
 * @version $Id: Hex.java 1080701 2011-03-11 17:52:27Z ggregory $
 */
public class Hex {

	/**
	 * Used to build output as Hex
	 */
	private static final char[] DIGITS_LOWER = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd',
			'e', 'f' };

	/**
	 * Used to build output as Hex
	 */
	private static final char[] DIGITS_UPPER = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D',
			'E', 'F' };

	/**
	 * Converts an array of characters representing hexadecimal values into an array of bytes of those same values. The
	 * returned array will be half the length of the passed array, as it takes two characters to represent any given
	 * byte. An exception is thrown if the passed char array has an odd number of elements.
	 * 
	 * @param data
	 *            An array of characters containing hexadecimal digits
	 * @return A byte array containing binary data decoded from the supplied char array.
	 * @throws DecoderException
	 *             Thrown if an odd number or illegal of characters is supplied
	 */
	public static byte[] decodeHex(char[] data) throws Exception {

		int len = data.length;

		if ((len & 0x01) != 0) {
			throw new Exception("Odd number of characters.");
		}

		byte[] out = new byte[len >> 1];

		// two characters form the hex value.
		for (int i = 0, j = 0; j < len; i++) {
			int f = toDigit(data[j], j) << 4;
			j++;
			f = f | toDigit(data[j], j);
			j++;
			out[i] = (byte) (f & 0xFF);
		}

		return out;
	}

	/**
	 * Converts a hexadecimal character to an integer.
	 * 
	 * @param ch
	 *            A character to convert to an integer digit
	 * @param index
	 *            The index of the character in the source
	 * @return An integer
	 * @throws DecoderException
	 *             Thrown if ch is an illegal hex character
	 */
	protected static int toDigit(char ch, int index) throws Exception {
		int digit = Character.digit(ch, 16);
		if (digit == -1) {
			throw new Exception("Illegal hexadecimal character " + ch + " at index " + index);
		}
		return digit;
	}

	/**
	 * Converts an array of bytes into an array of characters representing the hexadecimal values of each byte in order.
	 * The returned array will be double the length of the passed array, as it takes two characters to represent any
	 * given byte.
	 * 
	 * @param data
	 *            a byte[] to convert to Hex characters
	 * @return A char[] containing hexadecimal characters
	 */
	public static char[] encodeHex(byte[] data) {
		return encodeHex(data, true);
	}

	/**
	 * Converts an array of bytes into an array of characters representing the hexadecimal values of each byte in order.
	 * The returned array will be double the length of the passed array, as it takes two characters to represent any
	 * given byte.
	 * 
	 * @param data
	 *            a byte[] to convert to Hex characters
	 * @param toLowerCase
	 *            <code>true</code> converts to lowercase, <code>false</code> to uppercase
	 * @return A char[] containing hexadecimal characters
	 * @since 1.4
	 */
	public static char[] encodeHex(byte[] data, boolean toLowerCase) {
		return encodeHex(data, toLowerCase ? DIGITS_LOWER : DIGITS_UPPER);
	}

	/**
	 * Converts an array of bytes into a String representing the hexadecimal values of each byte in order. The returned
	 * String will be double the length of the passed array, as it takes two characters to represent any given byte.
	 * 
	 * @param data
	 *            a byte[] to convert to Hex characters
	 * @return A String containing hexadecimal characters
	 * @since 1.4
	 */
	public static String encodeHexString(byte[] data) {
		return new String(encodeHex(data));
	}

	/**
	 * Converts an array of bytes into an array of characters representing the hexadecimal values of each byte in order.
	 * The returned array will be double the length of the passed array, as it takes two characters to represent any
	 * given byte.
	 * 
	 * @param data
	 *            a byte[] to convert to Hex characters
	 * @param toDigits
	 *            the output alphabet
	 * @return A char[] containing hexadecimal characters
	 * @since 1.4
	 */
	protected static char[] encodeHex(byte[] data, char[] toDigits) {
		int l = data.length;
		char[] out = new char[l << 1];
		// two characters form the hex value.
		for (int i = 0, j = 0; i < l; i++) {
			out[j++] = toDigits[(0xF0 & data[i]) >>> 4];
			out[j++] = toDigits[0x0F & data[i]];
		}
		return out;
	}
}
